Venezuela's largest union federation has called a 24-hour general strike in a show of support for striking managers from the country's state oil company.

The Confederation of Venezuelan Workers will hold the nationwide work stoppage on Tuesday.

Oil workers from the state-owned PDVSA are on the third day of a partial strike which has already disrupted fuel and gas supplies in the world's fourth-largest oil exporter.

The union's decision marks the biggest challenge to Venezuelan President Hugo Chavez since he came to power three years ago.

A general strike last December virtually paralysed the nation's economy.

Supplies hit

Union leader Carlos Ortega said the constant persecution of the country's workers by the government was sufficient reason to call the action.

Chavez: Not seen since strike began

He warned the 24-hour stoppage could be extended, depending on events on Tuesday.

The one million member union federation had been planning a general strike for later this month to call for higher public sector salaries. But the date was brought forward to coincide with the oil sector dispute.

Managers from PDVSA, marked the third day of their strike with demonstrations outside the company's buildings.

The oil strike was called to protest against the company's management board, which workers say President Chavez has filled with his supporters.

The progressive strike has shut down one of the company's refineries and affected fuel and gas supplies in the country.

Oil tankers are not being loaded, which may already have begun to affect the country's exports.

Falling popularity

This is a particular blow for the economy, as oil brings in almost half of the government's revenues.

The strike has also caused clashes between supporters and opponents of the government, culminating in the deaths of two oil workers last week.

If successful, the general strike will be a massive personal blow for Mr Chavez.

The president's popularity has plummeted in recent months following a successful nationwide strike last December.

Mr Chavez has not been seen in public since the oil strike began, and negotiations have broken down.

The government has taken a hard line against the oil workers so far. But this latest challenge may force them back to the table.